Telephone or like system



Feb. 18, 1947. c. GlLLlNGS ET AL 6 9 TELEPHONE OR LIKE SYSTEM 1 Filed Dec. 31, 1943 5 Sheets-Sheet 5 I INVENTORS CHARLES v sn.| m as LAWRENCE JOHN MURRAY ATTQBNEY Feb; 18, 1947.

c. GILLINGS EI'AL TELEPHONE OR LIKE SYSTEM Filed Dec. 51, 1943 5 Sheets-Sheet 4' INVENTORS 10GSP IOGTP' IGTPI 1e? 202ml ATTORN Y:

TELEPHONEYOR LIKE SYSTEM Fil ed Dec. 51, 1945 5 Sheets Sheet 5 INVENTORS CHARLES GILLINGS LAWRENCE JOHN MURRAY ATTOR NE Y Patented Feb. 18, 1947 TELEPHONE OR LIKE SYSTEM Charles Gillings and Lawrence John Murray,

Liverpool, England, assignors to' Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application Becembe'rfil, 1914s, Serial No. 515,323

' In Great Britain Februarydf), 1943 The present invention relates to telephone or like systems and is more particularly concerned with automatic telephone systems of the type disclosed in our application Serial No. 513,370, filed Dec. 8, 1943, in which the crossbar switch mechanisms provided at the various switching stages, viz. the group and penultimate selecting stages, have associated therewith control equipment adapted to receive the requisite dialled rigid or digits, and in response thereto to affect the setting up of the'associated crossbar switch. Each crossbar switch can handle more than one con nection and where two or more connections are to be set up through any one'switch, the associated control equipment will be repeatedly utilised to enable these connections successively to be set up.

In the case of -inulti -exchange working a crossbar switch serving in anincoming group selecting capacity will terminate a number of junc tion lines corresponding to the number of connections which it can accommodate, and in these circumstances difficulties arise in ensuring that when the associated control equipment is han dling the setting up of a connection from one incoming junction, the distant or originating ends of the other junction lines concerned shall be suitably informed.

The object of the invention is to enable these diificulties to be overcome in a simple and effi'cient manner.

According to the invention a crossbar selector unit adapted to serve a number of incoming junction lines and having a control circuit individual to the unit and adapted to control the selector unit to set up one call at a time from any junction line to an idle line in a group determined by the number of impulses in a series transmitted to said unit is so arranged that in order to prevent impulses being transmitted over two or more of said junction lines simultaneously, a signal circuit extends over each junction circuit from the crossbar selector unit by which signal circuit the con trol circuit is enabled" to indicate when a junction line is inreadiness for the transmission of impulses thereover. In one example impulse regenerators are provided at the outgoing end of each junction line which regenerators are adapted to store the impulses transmitted to the line when a signal is received from the control equipment.

In another example all the idle junction lines having access to a group selector unit are rendered unavailable while the control circuit is in has been selected.

9 Claims. 1 (c1. fives-.22)

The invention will be better understood from the following description of two methods of car rying it into effect, reference being had to the accompanying drawings comprising Figs. 1-6." f

Figs, 1-4 when arranged in the manneriindi- V disclosed inlFigs'. 5 and 6, Fig. 5 showing theelements of an outgoing auto-to-auto impulse re'.-. peating'relay set' adapted to mark; itself as busy in response to a junction busy signal from the distant incoming end, while Fig. 6 shows the modifications which are necessary to the incoming crossbar group selecting unit .of Figs. 1-4, to enable junction busy signalling to be carried.

out whenever the associated control equipment is in use,

In'the circuit diagrams the number of contact units carried by each relay isv shown underneath its designation, as forinstance Fig. 1, the contact units being designated individu'ally in small letters which in this instance will be lkl, I k2 and ms. A'slow-to-release relay' is shown with a hatched portion at one end of. the rectangle indicative thereof, while aslow-tooperate relay is shown with a cross at one end; such a relay being in some instances slow-to release as well as slow-to-operate.

As regards the crossbar vertical and horizontal relays, theseare each indicated by-a' hatched rectangle, the contact units individual thereto being indicated in the same manner as for ordinary relays. The sets of crossbar switcl1;,cc n-- tacts proper which are closed atthe intersectionof any given pair of horizontal and vertical bars,

say controlled by relays IGSP (Fig. l); and IGS H- (Fig. 2), are designated and so on for each set of contacts involved.

.(3f the various unieseloctors such as the con.-.

trol group digit switch which will be referred to as DS, the various sets of wipers and banks are designated DSl, DS2 etc, The driving magnet which is indicated by a hatched square will, in this instance, be designated DM, and the magnet interrupter contacts will be designated dm. In the case of the digit switch DS, since the num-i ber of positions required is considerably less than the twenty-five available, they are arranged to make two appearances on the banks thereof so that this switch will have two home positions,

1 and 12. I v 1 Referring now to the trunking diagram of Fig;

4a, the crossbar group selector unit will be hereafter referred to as a group selector, although in fact it serves as a number-of group selectors in the accepted sense of the phrase. It preferably comprises two crossbar switching units with their vertical bars in efiect coupled together as shown to form a group selector. More specifically, the coupling will be efiected electrically by'the conmotion of each column of vertically commoned contact springs of the spring sets in one unit with a corresponding column of-vertically com-,

1 m'oned contact springs on the other unit of the pair. l The selector is. of the l0-level -outlet per level type and is capable of handling ten connections; and for this purpose ten incoming junctions from distant exchanges can be served therebyv and will connect with the horizontal bar relays IGSP-IGSP. The horizontal bars provided for the, purpose. of determining the selected one of the ten possible levels are controlled by the relays lG'I'P-IDGTP and the two sets of ten vertical hold relays IGSH-ZUGSH and lGTH-ZUGTH when operated in pairs such as IGSH and IGTH or ZGSH and ZGTH and so on and in conjunctionwith one incoming and one level selecting relay, enable the two units of the pair forming the group'selector switch proper to function to connect an'incoming junction line via a free internal link within the selector to a free one of,

the twenty outgoing external links accessible from a selectedlevel of the selector and extending to a succeeding switching stage. I

Referring now to the circuits of Figs. 1-4, circuits of the group selector which will be termed Q'SU are shown in the upper'parts of Figs. 1 and 2, while circuits of the control group or equipment which will be termed GCG are shown in they lower parts of these figures and in Figs. 3 and 4.

In the group selector circuit there is shown the horizontal prepare relay IGSP together with the auxiliary relays IGSR, lKand INF associated withthe first out of the ten possible incoming junctions to theselector, which relays, in common with the correspondingrelays of the nine other incoming junctions have access over common leads Ill-l4 to the control group GCG. Fori junction busying purposes, as will be later appreciated, the relays IGSP-"IGSP associated with the ten incoming junctions are arrangedin a chain-switching circuit, of which relays IGSP,

ZGSP and IUGSP are shown. In'addition, the vertical hold relays IGSI-I and IGTH of the first vertical internal link and horizontal prepare re- 1 lay IGfIP associated with the first of the ten possible outgoing levels are also shown.

The control group GCG comprisesa set of reverse-drive electromagnetically operated type, the

ing one of the level selecting relays. lGTP-IUGT? '70. lays and three uniselectors, of the 25-point re- 4, is operated. One or other of the outlet control switches AOS or BOS, according to whether digits- 1-5 or 6-0 are dialled, is then caused to test over the twenty outlets of the selected outgoing level, and in accordance with the particular outgoing outlet taken into use a particularone of the twenty pairs of vertical hold relays is operated to switch the connection through and the control group is then released for further use in piloting a subsequent call through the same group selector. v

Considering now the taking into use of the group selector, there will be provided at the outgoing originating end of each of the junctions a relay set provided with impulse storage and retransmission facilities, the re-transmission being adapted to be initiated only in response to a signal from the distant incoming end of the junc- On the seizure of this relay set via a preceding selector train, an earth potential is extended forward over the negative junction wire, while a battery potential via the winding of a relay is extended forward over the ositive junction wire.

At the incoming end of the junction the negative lead connects with the relevant horizontal prepare relay, IGSP inthis instance, where the first one of the ten possible junction lines served by selector GSU is being considered. This relay is connected via contacts lgspZ and n3 and chain connected contacts l0gsp3.lgsp3 to battery via resistance YA. It will be noted that there is no standing earth connection to'the positive line so that the relay in the outgoing relay set cannot yetoperate. At the group selector end of the junction, if no other call is in process of being set upon selector GSU, "none of the relays 2GSP-IIIGSP will be operated, and relay IGSP can therefore operate and at its make-first light contacts lgspl completes a local locking circuitfor itself, whereupon it actuates its associated wardly to operate relay A on its left-hand winding.

The connection of relay A to the positive line enables the waiting relay at the outgoing end to operate, and when it does so, the outgoing relay'set is conditionedior sending out any trains of dialled impulses which it receives. Meanwhile, relay A in operating at contacts a! (Fig. 3) operates relay B in series with rectifier MRA to battery via resistance YG. Relay B in operating at contacts b! provides an earth potential for the DM magnet impulsing circuit, at contacts b2 completes an energising'circuit for relay 0 in series with resistance YH and magnet DM (nonoperative inthis condition), at contacts M (Fig. 1) extends to an earth on to commonlead Iil so as to bring up relay IGSR and-at contacts b5 brings up relay BB. The group selector relay [GSR in operating at contacts lgsrl disconnects relay I GSP from the incoming negative lead and completes a local locking circuit therefor, while atc'oiitacts|'ysr2"(Fig.12)' it extends the' left-hand wiiidingof relay A to the negative conductor and this relay now holds on both its windings to the loopextended forward from the distant outgoing relay set, and subsequently responds 'to"the first train of impulses to be re=transmitted therefrom: Relay BB in operating at contacts bbl connects thecentre winding of relay TA to common lead S, its other contacts having no function at'this stage. Relay C in operating at contacts cl (Fig; 3) prepares for the reception of thegroup selecting digit on magnetlDM orswitch DS. l In case the calling party should neglectto dial the group selecting digit,the common equipment GCG will be held *unnecessa'rily'and relay ilGSP (Fig. .1). in remaining operated will prevent any of the other I relays ZGSP-III GSP' from being operated by calls received over any. of thenine remaining incoming junctions to theg'roup selector G817, and so will prevent a call being set up from any of these sources. Arrangements are therefore made to release equipment GCG and to return a busy tone to the calling subscriber if the group selecting digit is not dialled within a predetermined periodafter seizure of the equip: ment GCG. The timing of this period is effected by the use of a pair of relays TA and 'IZ (Fig. 3) in conjunction with a delay set (not shown) which is" common to the exchange and which is arranged to supply earth pulses bearing a definite time relation to common leads S and Z. On operation of relays Band BB-when control group GCG is taken into use, contacts bbl (Fig. 1) connect the centre winding of relay TA to the S leadand' if the delay set'is in'its normal position, an earth will be encountered on this lead and relay TA will operate." At contacts tal it connects its lefthand winding and the lower-winding of relay T2 to the Z lead, while at contacts ta2. it looks to earth overits right-hand winding. At contacts t'a3 it extends earth on to the delay set start lead ST. After the predetermined period an earth pulse is applied from the delay set to the Z lead, whereupon relay 'IZ operates and at contacts tzl removes the short-circuit from-its upper winding over which it locks to the earthed contacts bi-vla' resistance YB. At contacts tz2 'and tz3 the initial locking and operating circuits for relay TA are opened, but this relay remains held via the lower winding of relay TZ. At contacts tz2 earth is extended over common lead 1410 bring up relay INF (Fig. 2) on its left-hand winding. At the end of the Z pulse relay TZ remains held' and relay TA releases. fR'elay INF in operating at contacts opens theoperating and locking circuit'for relay IGSP, at contacts |nf3 and lnfl connects its outer windings across the incoming speaking conductors' and at contacts lnf5 a number unobtainable tone is connected up over common lead N -I'E'to the centre winding of relay INF from whence it is transmitted to the calling party; Relay. "I'GSP in releasing releases lGSR,'re-completes the GSP relay chain current and also re-, leases relay A in the control group, Relay A in releasing initiates the release of the control group in a; manner along the lines to be described'later, and this group is now ready to handle'a subsequent; call through: the group selector; RelayJlNF remains held untilthe calling party hangs up and whenhe does so relay INF releasesand' a'tcontacts I'nfl .re-prepare'sfl an operatin eircuit{for'relay' IGSP for use when a calling party 'o'riginates another call over this junction. Hit the calling party dial's the group selecting 6 digit -within the allowable predetermined :period after'the' taking into use 'ofgroup GCG, on the first release of relay A an energising circuit is completed for magnet DM as follows: earth, con.- tacts b1 and cl, left-hand low resistance wind-1 ing of :relay C,- magnet DM to battery, the wind ing' of .relay B being short-cir'cuited during this time,=while.the right-hand winding'of relay C is similarly short-circuited inserieswith resistance I YH. On' the: re-operation of relay A .at the end of 'the first impulse of the received train, an

' energising circuit is recompleted-ior relay B and relay C nowv holds operated on both its windings in series with magnet DM whichwill nothold in this condition, and which thereupon releases to :advance'its wipers tocontacts 2 or l3 accord ings'to which half of the. banks is beingused; 'An operating circuit is now completed forrelay :N over wiper and bankDSl, operated contacts bb'l, bank and wiper AOSI and operated contacts 02 and D3 to battery via resistance YF, and thisrelay at its contacts nl completes a local locking circuit foritself. At contacts n2 it opens the holding circuit for relay C, and at the same time short-circuits its right-hand winding so that should there be no second pulse of the train,-as

willbe assumed in the present instance, relay-C will release after a slow releaseiperiod governed by the short-circuiting of. its winding and will initiate hunting for a free outlet to a succeeding group selector in a manner to be shortly de-;

scribed.

Relay B willhave held operated during the single received dialled impulse and it. may be mentioned here that the presence of the metal rectifier MBA in its initial energising circuit serves to prevent the slowing up of the magnet DM which wouldotherwise result from the di-' rect connection of a comparatively low value non-inductive resistance such as YGracross its winding; neither magnet DM nor relay 0 moretacts'n4-and b6- and wiper. DS4 which will bein position? or 13 when digit 1 has been dialled;- whereupon the crossbar relay IGTP will be oP- erated'to operate the horizontal bar associated with the first one of the ten levels of outlets;

Contacts cl (Fig. 3) open the impulsing circuit; while contacts 02 and 03 complete a self-inter rupted driving circuit for magnet AOM or BOM according as to whether digitl-5'or. 6-0 has been diallecL- In the present instance magnet AOM willbe set in operation, whereupon the. AOS wipers are caused-to test over the twentyroutlets "of the selec'toroutgoing level i in the fol lowing manner. On' the operation of relay'BB-g contacts bb2 (Fig. 3) connect upthe dual test ing cut-drive relay KR. via contacts of the group selectorwerticai hold relays lGTH-ZHGTH to corresponding contacts 2-2! on banks A082 and 3082. The associated switch wipers are inturn connected u r'over contacts heal and wiper bank D8 to any-one of the wipers AOSd-AIOS8; BOS I-BOSB. according to the position to which sWitchDShas been set, :i; efiiiniaccordance with" the value of the receiveddigit, In: the present instance where 1 has been -dialled,*-wipers A082 and BOSZ will be. connectedup: viawiper.

DS3 in position 2 or 13 towiper'AOS4, the bank.

sistance winding: ofrelay N, contacts. IcrZv and Icrrl, wiper DSZ in position 2. or 13, contacts bb5, bank and wiper AOSI, contacts 02, magnet interrupter contacts dam and magnet AOM- to battery. If the first outlet on the selected level I is free, anidle resistance marking battery-will be "encountered on lead ll, this battery bein extended thereon from the commonequipment associated with the succeeding selector, whereuponjrelay KR will rapidly operate and will open the magnet driving circuit at contacts lcr2 (Fig. 3)." If this outlet is busy, then switch AOS will rotate its wipers until a free outlet is encounteredwhereupon relay KR will operate and function as described. It is also possible for the first outlet on level I to be free and at the same time for the first outlet on another level or levels of the same crossbar selector to be busy, in which case the first, vertical internal link within'the crossbar switch will already be in use and itis therefore necessary to make this outlet test as busy to the hunting switch ADS. This is done by means of the contacts lgth2-2Bgth2 (Fig. 3)

in the operating circuit of relay KR sothat if outlet I! were free, but if at the same time the first vertical internal link were busy, relay IGTH wouldbe operated and the idle marking battery would be unable to reach relay KR, since the circuit thereto would be opened at contacts lgthz.

' remain held without appreciably restrainingzthe In the next position of switch AOS, contacts 2 gth2 become efiective'todetermine whether or not the second internal link is busy and so on.-

Assuming that the outlet I7 is taken in use,

relay KRin operating in-. addition to opening the magnet driving circuit also at contacts krZ completes an operating circuit for relay KRR-and at contacts krl extends an earth forward over the upper low resistance winding of relay KR to guard the outlet seized. -Relay KRR in operatingat contacts krrl im- 3 ther disconnects the magnet driving circuit, at contacts krr'2 prepares for the known dual test ing function of relay KR in case two or-more control groups should happen simultaneously to test on. the same outgoing link, thisfunctionbe ing described in our above-mentioned application; while contacts krr3 prepare to maintain relay KR operated independently of the crossbar vertical holding relay contacts lgth2. Contacts krrd (Fig. 1) extend earth upover common leadll to operate relay IK, contacts le -r5 and-701176 (Fig. 2) disconnect r'elayA from across. the incoming speaking conductors. while contacts lcrrl extend earth via wiper A083 inpositi'on 2;and.-lead IE to operate the crossbar relay IGSH and thisrelay in operating at its contactslgshl completes an operating circuit for the crossbar relaylGTI-I.

The functions ,of these relays IK, lGTI-l will be described later.-

.RelayA in releasing atcontacts al';(l1"ig;-3) short-circuits and releases relay; whereuponat contactsb5 (Fig. 1) relay BB is released, at contactsb4' relay IGSR, is released and at contacts I GSH and b& (Fig. '2) relayiG'I'P is released. -On release a oi=:re1ay.BB, contacts- Z1113 openithe-circuit of relay KR which in releasing.- brings- :downrelay Furthermore,=-at contacts bbfi-and bb'l (Fig. ;3) a homingcircuit is completedfor switch DSvia' the-earthed low resistancev winding; of relay N and. wiper and bank DSi and at contact bbisa homing circuit is completed for switch AO'S from the same earth; When both of these switches reach-their home positions, the homing circuit.

for relay N is opened at wipers and banks DSI and A081.

when-relay lGSPisreleased on operation of relay lK'as will belater described, none of the relays lGSP-"JGGSP can be i e-operated. until such time as the control-group is completely restored to normal as indicated bythe release of relay-N. Meanwhile, in the group selector; relay I'K'in operating at contacts llcl opens the holding circuit f@l":lB1EtY-|GSP and this relay releases. Ric-1' lays IGSH and .lG'II-I in'operatingoperate their associated vertical bars which together constitute the first vertical internal link within the crossbar unit, whereupon the sets of contacts restoration of the horizontal barswhich takes place on release of relays IGSP and lGr'li'P. 0111' release of relay KRR in the control equipment; the operating circuits of relays IK, IGSH and IGTI-I are opened, but before relay KRR is released following the release of .relays-Aand B. BB and KR, an earthwill have been returned back over the P lead (Fig. 2) from the succeeding selector in response to its seizure so that these relays will remain held throughoutthe setting up of the succeeding switches of the train, and then throughout theensuing conversation.

If now another call should arrive over the junction line terminating on relay ZGSP this relay will operate and lockover its contacts 2gspl, while at, its contacts ZgspZ and 2ysp3 the other relays of the chain are prevented from operating. .Whenrelay K58? and its associated relays are connected through to the common group GOG; relay A will be connected to the junction and will 0P- crate the waiting relay inthe'calling outgoing relay set to allow of the re-transmission of'the group selecting digit as andwhen it is desired.

If .tWO or more calls arrive simultaneouslm-gthe GSP relay with the lowest prefix number will in,

operating out out, the other GSP relay or relays involved and the other call or callswill have to wait until the control group again comes free when the process will be repeated if more than one call wishes to switch in to the control group.

Incase acall arrives over a junctionwhile the common equivalent GOG is in use the associated relays in-the group selector will be'unable tocon+ nect with the common equipment and relay -A will not be connected to the junctiomso that on the dialling oi the group selecting digit and any During-the homingv of these switches it will be noted that contacts n3=(Fig. I) maintain the GSP relay'chain circuit open so that even going relay set until such.time as the control equipment becomes free and can be taken into use when re-transmission can take place as described.

Returning now to the search for a free outlet by switch AOS, if all outlets prove to be busy, switch AOS will rotate its wipers to contacts 22 where a battery potential via resistance YJ will be encountered which feds back over bank and wiper A084, bank and wiper BS3, contacts bb3 and wiper and bank AOSZ to bring up relay KR. Re-

lay KRR functions as before described with the exception of contacts krr'l (Fig. 2) which extend earth over wiper AOS3 in position '22 and then over common lead I4 to bring up relay INF. RelaylNF in operating at its contacts lnfl discon- 'nects the locking circuit for relay IGSP, at contacts lnf2 completes a local locking circuit ,for relay lK which will have been operated over lead .H. at contacts lnj3 and. in connects itself across the incoming speaking conductors and at contacts lm5 a busy tonesource over common lead BTE is connected up via contacts lk3-to the centre winding of relay INF from whence busy tone is transmittedto the calling party. During this time the common control proceeds to release normalmanner so as to be available for use in setting up further calls on the groupselector .When the calling, party subsequently hangs up after. receiving the busytone, relay INF releases and releases relay [Kat contacts'l'nfz, while at contacts, Inf relay IGSP is re-connected to the incoming junction negative lead in readiness for the 'sett'ingup of a further call by this subscriber.

? Considering now the second method of carry-,

ing the invention into efiect, reference should be ,had to Figs. 5 and 6.

As previously mentioned, Fig. 6 merelyshows the modifications which are necessary to the incoming crossbar group selector already described to enable junction busy signalling to, be carried loutwhenever the associated control equipmentis in use, the modifications involving extra contacts I704, bland 11.5 on relays lK, B and N. Contacts H whi w e pr io l in-o din y an overbombination are now a make-before-break changeover combination; an additional common lead l8 between the group selector and its asso- Tciated equipment GOG is alsoprovided.

When the outgoing relay set of Fig. 5 is taken into use, relay TB, which in conjunction with its non-inductive resistance shunt forms the idle marking resistance battery, is operated by earth extended ,forw'ard over the P lead from the testing relay in the preceding stage. This relay in operating at its contacts tbl disconnects the junction busy" relay JCB from the outgoing junction positive lead and connects earth thereto. This earth extends forward to the incoming selector of Fig. 6 and then over contacts l kt and 'lgsr3 to common lead" l8 from which lead it extends back to the positive leads of all the other incoming" junctions terminating 0n the-selector andbrin'gs about the operation of the JCB relays atthe outgoing end'sof these junctions. The UCBrelays .in'operating, at their contacts iicbl disconnect the standing idle marking batteries via the relays TB and so mark-their respective outgoing relay sets as busy to the group of selector switches which have access to suchjunctioiisL' V 1 I I 7 When the subscribers loop is extended forward lto the outgoing relay set, relay 9A operates and eln f n acts 9 bnnss u relay QB- R lay 0B ob3 operates relay JX. Relay JX in operating at-contaots a'xl completes an energising circuit for the slow-to-operate relay JZ, and at contacts 7:102 extends earth over contacts OM and the windings of relays D and I to the outgoing junction negative lead and at the distant incoming end this brings-about the operation of the crossbar horizontal relay IGSP. 1

When relay JZ operates after its slow period, it completes a local locking circuit for itself and opens the energising circuit for relay TB at contacts :izl, while at contacts :iz2 it opens the circuit for relay JX which commences to release slowly. On release of relay JX, relays D and I remain connected via contacts OM and 7'23 across theoutgoing loop in readiness for the repetition of trains of impulses and of subsequent supervision of the progress of the call.

Meanwhile, at the distant end the operation of relay IGSP brings about the operation of relay A in the associated common equipment onits left-hand winding and relay A in operating brings,

up relay B which at contacts b4 completes an operating circuit for relay lGSR. and at bl main! tains the junction busy" earth on to common lead I8 which connects with the positive wires or the incoming junctions to the group selector.

Ojn'operationof relay IGSR contacts Igsrhlocli coming end and the circuit will be ready to re c'eive trains of impulses. r W On each train of impulses relay OAat the outgoing end responds, and at itscontacts oa2 repeats these out over the junction, relay 00 being operated during each train toshort-circuit relays D and Iso as to provide an impedance-free im-E.

pulse-repeating loop The operation or the ina coming group selector in response to the received train of impulses is as already described. v When the call has been set up through the group selector GSU, the common equipment GCG is released by the operation of relay KRR therein, whereupon relays A and B release in turn and restore relay IGSR. Relay lGSR in restoring does not now reconnect common lead ill to the positive line of the junction in question, since relay IK in the group selector will have been operated, and at contacts lkl, will open the circuit until thecall is subsequently concluded. During the release of the control equipment, relay N maintains the junction busy" earth at contacts n5on common lead I8, but when relay N restores the earth is removed, whereupon the JCB relays at the outgoing end of all the other junctions incoming to the group selector arereleased and restore the idle marking batteries on to thein-J coming P leads of their associated outgoing ime pulse repeating relay sets in, readiness for a further call over one of these junctions to the in-' coming group selector. Whatwe claim as new and desire to secure by Letters Patent is: 1. Ina switching system having a plurality or independent impulse'transmitters, a pluralityol' carcass on any one of said primar-y lines for transmitting a signal from'said control unit backover that s primary line to causethe impulse transmitter corresponding thereto to begin transmitting impulses over that line to said control unit-and means; in said unit controlled by said impulses for selecting-a group of-s'e'eonda-ry lines in accordance-with said impulses and operatingsaid crossbar switch to connect said one primary line to; a secondary- -line in the selectedgroup.

2'.-In--a switching system having-a plurality of independent impulse transmitters, a plurality of prim-erylines corresponding respectively to said impulse transmitters, a plurality of groups of secondary lines, a crossbar switch inwhich all "of said lines terminate, a control unit for said ondition on any one of said primary lines for tie Srnitti-ng a signa-l from said control unit back over that primary linen-to cause the impulse "transmitter correspondingthereto to begin trans- 7 inaccordance with said impulses'andj'operating staid" crossbar-switch to connect' 'said one primary line we secondary line in the selected group, and m ans preventing saidfir'st means from transmittingjsignais from said "control unit back over ny two of said primary lines simultaneousgarizlie ssfoffthe time relationship in which calling-conditions appear on such two primary 3; In a switching system having a plurality of independent impulse transmitters, a plurality of primary lines corresponding respectively to'said impulse transmitters, a plurality of groups of sc'iondary -li'nesj"acrossbar switch in which all of said line's terminate,-a control unit for; said switch, means normail'y controlled by aoa'llin'g conditionon any one f"s'a}i'd"prinfary lines for causing the impulse transmitter corresponding to that-line to transmit impulses over such' line to said control unit, means in said-"unit controlled by said impulses for-selecting a group of Secondar-y ine's m? accordance with said impulses and operating said crossb-ar- 'switchto connectsaid one primary line-tea secondary line in the selectedgroup, and means preventing impulses from' being transmitted to said control unit con: currently by two of' said transmitters 'over' their respectively "corresponding primary lines.

L lla-In a, switching system, a crossbar switch having a plurality of incoming'lines and =a'p1urality-of outgoing lines, a control unit individual to said switch, means controlled by a calling condition "on any one of said incoming lines 'for conditioning said unit to receive impulses over that vline and for'then: reverting a signalover said line to initiate *the transmission of impulses to said control unit, and means in said control unit for operating said crossbar switch selectively in, accordance with the impulses thereafter received'over said incoming line, thereby to connectisaid line to a selected one of said-outgoing lines.

A switching system as claimed in claim 4, wherein each of said incoming unes has an individual storage device in which impulses are stored at. times, andkwhereineach of said devices 7 switch; -means--norma-l1y controlled by a calling 7 transmits such stored impulses over its associated line to said control unit responsive to said sig rial being reverted ovr' that li-ne" ing a plurality of incominglines and a plurality of outgoing lines, acontrol unit individual tosaid switch, meanscontrolled by a calling condition on anyone of saidincoming lines for conditioning said unit to receive impulses over that line; said means effective in the eventlthat a calling condi-= tion appears simultaneously on twoof said incom ing lines to condition said unitfirst to receive impulses over a particularpne of said two lines'and, after said impulses have been received, to condition said unit to receive impulses over the other of said two lines,-means operated when said control unit has been conditionedto receive impulses over any oneof said incoming lines to revert a signal over such lin'eto initiate the transmission of impulses to said unit, andinea'ns insa-i'd con= trol unit for operating said crossbarsvvitch selectively in accordance with the impulses over any incoming line thereby to connect such incoming line with a selected one of said outgoing lines,

7. In a switching system,"a crossbar switch havinga plurality of incoming lines and a plurality of outgoing lines,*a control unit individual to said switch, means normally controlled by a calling conditio-n'onfany 'one'o f said incoming lines for conditioning said-unit tofr'eceive impulses over that line and for th'en reverting a signal over said line to initiate the transmission "of; impulses to said control" unit, means in said control unit for operating said crossbar switch selectively in ac: cordance with theimpulses thereafter received over said incoming line, thereby to connect-said line to a selected one ofsaidoutgoing lines, and means efiective, in the event that a calling condition appears on any other incoming linewhile said impul'ses are being received over said one incoming line, to prevent said first means from re verting a signal oversaid other-'i-ncoming line-until said crossbar switch has 'been operated to connect said one in omin -line to said-selected outgoin 8-. I Ina switching system; acro'ssbanswitch hav. ing a plurality of incoming lines anda plurality of outgoing lines,- a control unit -individual to said switch, means normal-1y controlled by a calling condition on any one of said incoming lines'foi' conditioningsaid unit to receivefimpulses over that line and for then reverting a signal over said.

line to initiate the trans-missionof a group of impulses to said controlunit, means in said control unit for 'receiving saidgroup" of impulses'a'nd operating-"said crossbar switch selectively in accord ance therewith, thereby to connect said than a selected one 'of said outgoing lines,' and means efiective, in the event thataoallmg' condition ap pears on anyother incoming line while said impulses are beingreceived-overpaid 'one' incoming V firstfm'eans from revertin'g'a signal over said other incomingfli 'ne until all the impulsesofjsaid group'h'ave been received. j 9. Ina switchingsystem,a'crossbarswittihhav ing a plurality of incomingflines' and a plurality of groups of "outgoing lines, "a control unit indie viduall to said switch, a conductor common toall of "said incoming lines, meansope'rated responsive to the seizure of any oneofsaid-inc'orning linest'o complete a guarding circuit-extending over "said conductor to said control unit thereby to'ite'mpbl aiily dis a-bI -the 'other---sali incomlng'flines, eans in sa d control imitoperated-'difectlvly over "the seized incoming line -to select a partlcu 6. In a switching-systemj acrossbarswit'ch hav H 2,416,093 13 e 14 Iar group of said outgoing lines, other means in REFERENCES CITED said unit then operated to search for an idle out- Th f n going line in the selected group and, when one is file 3 g f i are of record in the found, to operate said crossbar switch to connect the seized incoming line to said idle outgoing line, 5 UNITED STATES PATENTS and means thereupon operated to render said Number Name Date guarding circuit ineffective, thereby consequent- 130L931 Lundquist Apr. 21, 1931 1y to enable said other incoming lines. 1,991,193 Carpenter t 1 Feb. 12, 1935 2,034,883 Scudder Mar. 24, 1936 CHARLES GILHNGS- 2,253,743 Wicks Aug, 26, 1941 LAWRENCE JOHN MURRAY- 2,348,626 Holden May 9, 194

2,089,921 Carpenter Aug. 10, 1937 

